Cable Modem System And Method For Supporting Packet PDU Compression

ABSTRACT

A cable modem system and method are provided for using a data compression dictionary to transmit compressed payload data in a DOCSIS network while utilizing conventional cable modem termination system (CMTS) equipment. A cable modem system in accordance with the invention includes a cable modem and a CMTS adapted to send and receive compressed payload data. In one example, the cable modem is adapted to compress PDU payload data using a data compression dictionary and the CMTS is adapted to reconstruct the compressed PDU payload data that is received from the cable modem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to the following provisionalapplications:

Provisional U.S. Patent Application Ser. No. 60/239,525, entitled “Usingthe TDMA Characteristics of a DOCSIS Cable Modem Network to SupportExtended Protocols,” filed Oct. 11, 2000, by Bunn et al., (stillpending)(incorporated by reference in its entirety herein).

Provisional U.S. Patent Application Ser. No. 60/239,526, entitled“Dynamic Delta Encoding for Cable Modem Header Suppression,” filed Oct.11, 2000 by Bunn et al., (still pending)(incorporated by reference inits entirety herein).

Provisional U.S. Patent Application Ser. No. 60/239,524, entitled“Dynamically Mixing Protocol-Specific Header Suppression Techniques toMaximize Bandwidth Utilization in a DOCSIS Network,” filed Oct. 11, 2000by Bunn et al., (still pending)(incorporated by reference in itsentirety herein).

Provisional U.S. Patent Application Ser. No. 60/239,530, entitled“Efficiently Transmitting RTP Protocol in a Network that Guarantees InOrder Delivery of Packets,” filed Oct. 11, 2000 by Bunn et al., (stillpending)(incorporated by reference in its entirety herein).

Provisional U.S. Patent Application Ser. No. 60/239,527, entitled“Packet PDU Data Compression within a DOCSIS Network,” filed Oct. 11,2000, by Bunn et al., (still pending)(incorporated by reference in itsentirety herein).

Provisional U.S. Patent Application Ser. No. 60/240,550, entitled “CableModem System,” filed Oct. 13, 2000, by Bunn et al., (stillpending)(incorporated by reference in its entirety herein).

This application is related to the following non-provisionalapplications, all having the same filing date as the presentapplication:

“Cable Modem System and Method For Supporting Extended Protocols,” U.S.Patent Serial No. TBD (Attorney Docket No. 1875.0650001), by Bunn et al.filed concurrently herewith and incorporated by reference herein in itsentirety.

“Dynamic Delta Encoding for Cable Modem Header Suppression,” U.S. PatentSerial No. TBD (Attorney Docket No. 1875.0640001), by Bunn et al., filedconcurrently herewith and incorporated by reference herein in itsentirety.

“Cable Modem System and Method for Dynamically Mixing Protocol-SpecificHeader Suppression Techniques,” U.S. Patent Serial No. TBD (AttorneyDocket No. 1875.0660001), by Bunn et al., filed concurrently herewithand incorporated by reference herein in its entirety.

“Efficiently Transmitting RTP Protocol in a Network that Guarantees InOrder Delivery of Packets,” U.S. Patent Serial No. TBD (Attorney DocketNo. 1875.0670001), by Bunn et al., filed concurrently herewith andincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to communication systems.More particularly, the present invention is related to cable modemsystems and methods for transferring data between a cable modem systemand a cable modem termination system.

2. Background

In conventional cable modem systems, a hybrid fiber-coaxial (HFC)network provides a point-to-multipoint topology for supporting datacommunication between a cable modem termination system (CMTS) at thecable headend and multiple cable modems (CM) at the customer premises.In such systems, information is broadcast downstream from the CMTS tothe cable modems as a continuous transmitted signal in accordance with atime division multiplexing (TDM) technique. In contrast, information istransmitted upstream from each of the cable modems to the CMTS as shortburst signals in accordance with a time domain multiple access (TDMA)technique. The upstream transmission of data from the cable modems ismanaged by the CMTS, which allots to each cable modem specific slots oftime within which to transfer data.

Conventional cable modem systems are asymmetrical in that there isconsiderably less bandwidth available for upstream transmissions thanthere is for downstream transmissions. This lack of upstream bandwidthis further exacerbated by the fact that the upstream channels must beshared by multiple cable modems. As a result, the conservation ofupstream bandwidth is imperative in order to maintain overall systemperformance. This is particularly true where cable modem users areengaging in activities that require both substantial upstream anddownstream bandwidth, such as IP telephony, video teleconferencing andInternet gaming.

Conventional cable modem systems utilize DOCSIS-compliant equipment andprotocols to carry out the transfer of Protocol Data Units (PDU) datapackets between multiple cable modems and a CMTS. PDU data packets arecomprised of a header portion and a payload portion. The payload portionis the information intended to be transmitted from one point to another,for example, voice or data. The header portion contains protocolinformation identifying the source and destination of the payload. Theheader portion of the PDU data packet further provides instructions onhow to process the payload portion contained therein. The term DOCSIS(Data Over Cable System Interface Specification) generally refers to agroup of specifications published by CableLabs that define industrystandards for cable headend and cable modem equipment. In part, DOCSISsets forth requirements and objectives for various aspects of cablemodem systems including operations support systems, management, datainterfaces, as well as network layer, data link layer, and physicallayer transport for data over cable systems. The most current version ofthe DOCSIS specification is DOCSIS 1.1.

It has been observed, however, that the use of proprietary data transferprotocols that extend beyond those provided by the DOCSIS specificationmay be advantageous in conserving network bandwidth in a cable modemsystem. This is particularly true with respect to Payload HeaderSuppression (PHS). PHS, as defined by DOCSIS 1.1, allows for thesuppression of unnecessary Ethernet/IP header information in the headerportion of a DOCSIS packet by the cable modem and subsequentreconstruction of the header portion by the CMTS. The goal of PHS is toreduce the number of bits transferred per packet, thereby improvingnetwork bandwidth utilization. However, DOCSIS PHS only permits headersuppression based on the presence of redundant header bytes insequentially-transmitted packets. The above referenced patentapplications disclose ways to utilize more efficient payload headersuppression techniques in transferring data over a cable modem network.However, it is has been further observed that the DOCSIS protocol doesnot support data compression in the payload portion of the PDU datapackets. Many packets normally transmitted in the upstream direction ina DOCSIS network contain identical ASCII character strings in thepayload. Examples of these strings are “http://www.”, “POP”, “SMTP”,“GET”, and “PUT”. The network could be used more efficiently if thepayload of a given DOCSIS packet could be transmitted with fewer bytes.

Heretofore, the use of proprietary data transfer protocols that extendbeyond those provided by the DOCSIS specification have been avoided.This is due, in part, to the fact that the DOCSIS specification does notprovide a mechanism for using alternative protocols in a cable modemsystem. For example, the DOCSIS specification does not provide amechanism for the use of data packet formats other than those itprovides. Moreover, because conventional CMTS and cable modem deviceshave been designed in accordance with the DOCSIS specification, the useof extended protocols has been avoided to ensure interoperabilitybetween individual cable modem system components. For example,conventional DOCSIS-compliant CMTS equipment is incapable ofdifferentiating between standard DOCSIS traffic and traffic transmittedin accordance with an extended protocol.

Accordingly, what is desired is a system and method for transferringdata in a cable modem network that supports the use of protocols thatextend beyond the DOCSIS specification. More particularly, the desiredsystem and method should support the use of PDU payload datacompression. However, the desired system and method should beinteroperable with DOCSIS in the sense that components of a cable modemsystem that support PDU payload compression can exist on the samenetwork with components that do not. Furthermore, the desired system andmethod should require very little modification to existing cable modemsystem components, such as existing cable modem and CMTS equipment.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a cable modem system that allowsfor use of proprietary data transfer protocols that extend beyond thoseprovided by the DOCSIS specification. More particularly, the presentinvention provides a system and method for compressing PDU payload datatransmitted within a DOCSIS service identifier (SID). The CMTSidentifies a plurality of frequently occurring data strings within thePDU payload transmitted by cable modems in the DOCSIS network. The CMTSthen assigns a token to represent each one of the plurality offrequently occurring data strings. Each one of the plurality offrequently occurring data strings and each token assigned to representeach one of the plurality of frequently occurring data strings are thenentered into a lookup table of a data compression dictionary. The datacompression dictionary is then transmitted to all cable modems in theDOCSIS network.

Upon receiving a plurality of PDU data packets for transmission, a cablemodem searches the data compression dictionary for the data stringscontained in the payload portion of each PDU data packet. For each datastring stored in the data compression dictionary, the cable modemreplaces the data string with the token assigned to represent the datastring within the PDU payload. Next, the cable modem appends acompression indicator to each token. The compression indicator signalsthe cable modem termination system to look up the token in its datacompression dictionary. The cable modem then transmits to a cable modemtermination system, the plurality of data packets that now contain thetokens as their PDU payload. The cable modem termination systemidentifies the token representing the compressed PDU payload datastring. The CMTS then searches its data compression dictionary for thetoken to identify the corresponding expanded data string. The CMTS thenreplaces the token with the corresponding expanded data string. In thisway each data packet is restored to its original form.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 is a high level block diagram of a cable modem system inaccordance with embodiments of the present invention.

FIG. 2 is a schematic block diagram of a cable modem termination system(CMTS) in accordance with embodiments of the present invention.

FIG. 3 is a schematic block diagram of a cable modem in accordance withembodiments of the present invention.

FIG. 4 is a block diagram of a data compression dictionary in accordancewith embodiments of the present invention.

FIG. 5 is a flowchart of a method for generating a data compressiondictionary in accordance with embodiments of the present invention.

FIG. 6 is a flowchart of a method for compressing packet PDU data usinga data compression dictionary in accordance with embodiments of thepresent invention.

FIG. 7 is a flowchart of a method for expanding packet PDU data using adata compression dictionary in accordance with embodiments of thepresent invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION Table of Contents

-   A. Cable Modem System in Accordance with Embodiments of the Present    Invention-   B. Example Cable Modem System Components in Accordance with    Embodiments of the Present Invention-   C. Packet PDU Compression in Accordance with Embodiments of the    Present Invention

1. Data Compression Dictionary

2. Packet PDU Compression

3. Packet PDU Expansion

-   D. Conclusion-   A. Cable Modem System in accordance with Embodiments of the Present    Invention

FIG. 1 is a high level block diagram of an example cable modem system100 in accordance with embodiments of the present invention. The cablemodem system 100 enables voice communications, video and data servicesbased on a bi-directional transfer of Internet protocol (IP) trafficbetween a cable system headend 102 and a plurality of cable modems overa hybrid fiber-coaxial (HFC) cable network 110. In the example cablemodem system 100, only two cable modems 106 and 108 are shown forclarity. In general, any number of cable modems may be included in thecable modem system of the present invention.

The cable headend 102 is comprised of at least one cable modemtermination system (CMTS) 104. The CMTS 104 is the portion of the cableheadend 102 that manages the upstream and downstream transfer of databetween the cable headend 102 and the cable modems 106 and 108, whichare located at the customer premises. The CMTS 104 broadcastsinformation downstream to the cable modems 106 and 108 as a continuoustransmitted signal in accordance with a time division multiplexing (TDM)technique. Additionally, the CMTS 104 controls the upstream transmissionof data from the cable modems 106 and 108 to itself by assigning to eachcable modem 106 and 108 short grants of time within which to transferdata. In accordance with this time domain multiple access (TDMA)technique, each cable modem 106 and 108 may only send informationupstream as short burst signals during a transmission opportunityallocated to it by the CMTS 104.

The CMTS 102 further serves as interface between the HFC network 110 anda packet-switched network 112, transferring IP packets received from thecable modems 106 and 108 to the packet-switched network 112 andtransferring IP packets received from the packet-switched network 112 tothe cable modems 106 and 108 when appropriate. In embodiments, thepacket-switched network 112 comprises the Internet.

In addition to the CMTS 104, the cable headend 102 may also include oneor more Internet routers to facilitate the connection between the CMTS104 and the packet-switched network 112, as well as one or more serversfor performing necessary network management tasks.

The HFC network 110 provides a point-to-multipoint topology for thehigh-speed, reliable, and secure transport of data between the cableheadend 102 and the cable modems 106 and 108 at the customer premises.As will be appreciated by persons skilled in the relevant art(s), theHFC network 110 may comprise coaxial cable, fiberoptic cable, or acombination of coaxial cable and fiberoptic cable linked via one or morefiber nodes.

Each of the cable modems 106 and 108 operates as an interface betweenthe HFC network 110 and at least one attached user device. Inparticular, the cable modems 106 and 108 perform the functions necessaryto convert downstream signals received over the HFC network 110 into IPdata packets for receipt by an attached user device. Additionally, thecable modems 106 and 108 perform the functions necessary to convert IPdata packets received from the attached user device into upstream burstsignals suitable for transfer over the HFC network 110. In the examplecable modem system 100, each cable modem 106 and 108 is shown supportingonly a single user device 114 and 116. In general, each cable modem 106and 108 is capable of supporting a plurality of user devices forcommunication over the cable modem system 100. User devices may includepersonal computers, data terminal equipment, telephony devices,broadband media players, network-controlled appliances, or any otherdevice capable of transmitting or receiving data over a packet-switchednetwork.

In the example cable modem system 100, cable modem 106 represents aconventional DOCSIS-compliant cable modem. In other words, cable modem106 transmits data packets to the CMTS 104 in formats that adhere to theprotocols set forth in the DOCSIS specification. Cable modem 108 islikewise capable of transmitting data packets to the CMTS 104 instandard DOCSIS formats. However, in accordance with embodiments of thepresent invention, the cable modem 108 is also configured to transmitdata packets to the CMTS 104 using proprietary protocols that extendbeyond the DOCSIS specification. Nevertheless, cable modem 108 is fullyinteroperable with the DOCSIS-compliant cable modems, such as cablemodem 106, and with DOCSIS-compliant CMTS equipment. The manner in whichcable modem 108 operates to transfer data will be described in furtherdetail herein.

Furthermore, in the example cable modem system 100, the CMTS 104operates to receive and process data packets transmitted to it inaccordance with the protocols set forth in the DOCSIS specification.However, in accordance with embodiments of the present invention, theCMTS 104 can also operate to receive and process data packets that areformatted using proprietary protocols that extend beyond those providedby the DOCSIS specification, such as data packets transmitted by thecable modem 108. The manner in which the CMTS 104 operates to receiveand process data will also be described in further detail herein.

-   B. Example Cable Modem System Components in Accordance with    Embodiments of the Present Invention

FIG. 2 depicts a schematic block diagram of an implementation of theCMTS 104 of cable modem system 100, which is presented by way ofexample, and is not intended to limit the present invention. The CMTS104 is configured to receive and transmit signals to and from the HFCnetwork 110, a portion of which is represented by the optical fiber 202of FIG. 2. Accordingly, the CMTS 104 will be described in terms of areceive path and a transmit path.

The receive path begins with the receipt of upstream burst signalsoriginating from one or more cable modems by the optical-to-coax stage204 via the optical fiber 202. The optical-to-coax stage 204 routes thereceived burst signals to a radio frequency (RF) input 206 via coaxialcable 208. In embodiments, these upstream burst signals having spectralcharacteristics within the frequency range of roughly 5-42 MHz.

The received signals are provided by the RF input 206 to the splitter214 of the CMTS 104, which separates the RF input signals into Nseparate channels. Each of the N separate channels is then provided to aseparate burst receiver 216 which operates to demodulate the receivedsignals on each channel in accordance with either a Quadrature PhaseShift Key (QPSK) or 16 Quadrature Amplitude Modulation (QAM) techniqueto recover the underlying information signals. Each burst receiver 216also converts the underlying information signals from an analog form todigital form. This digital data is subsequently provided to the headendmedium access control (MAC) 218.

The headend MAC 218 operates to process the digital data in accordancewith the DOCSIS specification and, when appropriate, in accordance withproprietary protocols that extend beyond the DOCSIS specification, aswill be described in further detail herein. The functions of the headendMAC 218 may be implemented in hardware or in software. In the exampleimplementation of FIG. 2, the functions of the headend MAC 218 areimplemented both in hardware and software. Software functions of theheadend MAC 218 may be stored in either the random access memory (RAM)220 or the read-only memory (ROM) 218 and executed by the CPU 222. Theheadend MAC is in electrical communication with these elements via abackplane interface 220 and a shared communications medium 232. Inembodiments, the shared communications medium 232 may comprise acomputer bus or a multiple access data network.

The headend MAC 218 is also in electrical communication with theEthernet interface 224 via both the backplane interface 220 and theshared communications medium 232. When appropriate, Ethernet packetsrecovered by the headend MAC 218 are transferred to the Ethernetinterface 224 for delivery to the packet-switched network 112 via arouter.

The transmit path of the CMTS 104 begins with the generation of adigital broadcast signal by the headend MAC 218. The digital broadcastsignal may include data originally received from the packet-switchednetwork 112 via the Ethernet interface 224. The headend MAC 218 outputsthe digital broadcast signal to the downstream modulator 226 whichconverts it into an analog form and modulates it onto a carrier signalin accordance with either a 64-QAM or 256-QAM technique.

The modulated carrier signal output by the downstream modulator 256 isinput to a surface acoustic wave (SAW) filter 228 which passes onlyspectral components of the signal that are within a desired bandwidth.The filtered signal is then output to an amplifier 230 which amplifiesit and outputs it to the intermediate frequency (IF) output 212. The IFoutput 212 routes the signal to the radio frequency (RF) upconverter210, which upconverts the signal. In embodiments, the upconverted signalhas spectral characteristics within the frequency range of approximately54-860 MHz. The upconverted signal is then output to the optical-to-coaxstage 204 over the coaxial cable 208. The optical-to-coax stage 204broadcasts the signal via the optical fiber 202 of the HFC network 110.

FIG. 3 depicts a schematic block diagram of an implementation of thecable modem 108 of cable modem system 100, which is presented by way ofexample, and is not intended to limit the present invention. The cablemodem 108 is configured to receive and transmit signals to and from theHFC network 110 via the coaxial connector 332 of FIG. 3. Accordingly,the cable modem 108 will be described in terms of a receive path and atransmit path.

The receive path begins with the receipt of a downstream signaloriginating from the CMTS 104 by the diplex filter 302. The diplexfilter 302 operates to isolate the downstream signal and route it to theRF tuner 304. In embodiments, the downstream signal has spectralcharacteristics in the frequency range of roughly 54-860 MHz. The RFtuner 304 downconverts the signal and outputs it to the SAW filter 306,which passes only spectral components of the downconverted signal thatare within a desired bandwidth. The filtered signal is output to anamplifier 308 which amplifies it and passes it to a downstream receiver310. Automatic gain controls are provided from the downstream receiver310 to the RF tuner 304.

The downstream receiver 310 demodulates the amplified signal inaccordance with either a 64-QAM or 256 QAM technique to recover theunderlying information signal. The downstream receiver 310 also convertsthe underlying information signal from an analog form to digital form.This digital data is subsequently provided to the medium access control(MAC) 314.

The MAC 314 processes the digital data, which may include, for example,Ethernet packets for transfer to an attached user device. The functionsof the MAC 314 may be implemented in hardware or in software. In theexample implementation of FIG. 3, the functions of the MAC 314 areimplemented in both hardware and software. Software functions of the MAC314 may be stored in either the RAM 322 or the ROM 324 and executed bythe CPU 320. The MAC 314 is in electrical communication with theseelements via a shared communications medium 316. In embodiments, theshared communications medium may comprise a computer bus or a multipleaccess data network.

The MAC 314 is also in electrical communication with the Ethernetinterface 318 via the shared communications medium 316. Whenappropriate, Ethernet packets recovered by the MAC 314 are transferredto the Ethernet interface 318 for transfer to an attached user device.

The transmit path of the cable modem 108 begins with the construction ofa data packet by the MAC 314. The data packet may include dataoriginally received from an attached user device via the Ethernetinterface 318. In accordance with embodiments of the present invention,the MAC 314 may format the data packet in compliance with the protocolsset forth in the DOCSIS specification or, when appropriate, may formatthe data packet in compliance with a proprietary protocol that extendsbeyond those set forth in the DOCSIS specification, as will be describedin further detail herein. The MAC 314 outputs the data packet to anupstream burst modulator 326 which converts it into analog form andmodulates it onto a carrier signal in accordance with either a QPSK or16-QAM technique.

The upstream burst modulator 326 outputs the modulated carrier signal toa low pass filter 328 which passes signals with spectral characteristicsin a desired bandwidth. In embodiments, the desired bandwidth is withinthe frequency range of approximately 5-42 MHz. The filtered signals arethen introduced to a power amplifier 330 which amplifies the signal andprovides it to the diplex filter 302. The gain in the power amplifier330 is regulated by the burst modulator 326. The diplex filter 302isolates the amplified signal and transmits it upstream over the HFCnetwork 110 during a scheduled burst opportunity.

-   C. Packet PDU Compression in Accordance with Embodiments of the    Present Invention

1. Data Compression Dictionary

Traditional modem data compression techniques are not useful within aDOCSIS network topology. The most popular algorithm (LZW) requires adata compression dictionary to be dynamically constructed at run-time.This requirement forces both ends of the communications pipe to haveroughly equivalent CPU power. In a DOCSIS system, the CMTS CPU wouldhave to be 1000 to 2000 times faster than the average cable modem tokeep up with this dictionary processing. Thus, in accordance with thepresent invention, the cable modem 108 and the CMTS 104 are eachprovided with a data compression dictionary. The data compressiondictionary will now be described with respect to FIGS. 4 and 5.

An exemplary data compression dictionary is illustrated in FIG. 4. In anembodiment, the data compression dictionary is a predefined, fixedlookup table. The lookup table is comprised of a payload data stringsection 405 and a token section 410. The payload data string section 405is used to list ASCII character strings that are frequently found in thePDU payload portion of a DOCSIS data packet. PDU payload data is theessential data that is being carried within a packet or othertransmission unit. In most cases, the payload does not include the“overhead” data required to get the packet to its destination. However,to a communications layer that needs some of the overhead data to do itsjob, the payload is sometimes considered to include the part of theoverhead data that this layer handles. However, in more general usage,the payload is the bits that get delivered to the end user at thedestination. For example, where a user is surfing the Internet or WorldWide Web, many identical ASCII strings are transmitted. These ASCIIstrings include among others, “http.///www.”, “POP”, “SMTP”, “GET”, and“POP”. In embodiments of the present invention, each string in thepayload data string section 405 is associated with a binary token storedin token section 410. During compression, the binary tokens aresubstituted for the ASCII strings. This results in fewer bytes needingto be transmitted. The process of creating the data compressiondictionary will now be explained with reference to FIG.5.

FIG. 5 is a flowchart of a method for generating a data compressiondictionary in accordance with embodiments of the present invention.

At step 505, the ASCII strings to be entered into the data compressiondictionary are identified. In an embodiment, the CMTS analyzes the datastrings being exchanged between it and the cable modems in the HFCnetwork 110. The CMTS then selects the most frequently occurring datastrings for entry into the data compression dictionary. In this way, thedata compression dictionary is tuned for the particular HFC network 110in which the CMTS and cable modems are located.

At step 510, the CMTS assigns a token, for example, a binary token, torepresent the data strings identified in step 505. In an embodiment, themost frequently occurring data string is assigned the smallest binarytoken. The next most frequently occurring data string is assigned thenext smallest binary token and so on. In this way, the fewest number ofbytes are substituted for the most frequently occurring data strings.

At step 515, the CMTS enters each identified data string from step 505and its assigned binary token from step 510 into a lookup table. Themaximum width and length of the lookup table is determined by the amountof memory space allocated to the data compression dictionary.

At step, 520, the CMTS transmits the data compression dictionary to eachcable modem with the HFC network 110. In an embodiment, the dictionaryis transmitted to each cable modem during an initialization process(i.e., when the modem is connected to the network). In alternativeembodiments, the cable modem could be instructed to halt compression inreal time so that the CMTS can transmit an updated data compressiondictionary.

In accordance with the present invention, the cable modem 108 and theCMTS 104 are adapted to send and receive compressed data. For example,in accordance with embodiments of the present invention, prior totransmission over the HFC network 110, the cable modem 108 is adapted tocompress PDU payload data using a data compression dictionary and theCMTS 104 is adapted to reconstruct the compressed PDU payload data uponreceiving it. Alternatively, the CMTS 104 could be adapted to compressthe PDU payload data using a data compression dictionary and the cablemodem 108 would be adapted to reconstruct it. A method for PDU packetcompression and expansion will now be explained with respect to FIGS. 6and 7.

2. Packet PDU Compression

FIG. 6 is useful for explaining a manner in which packets are compressedby cable modem 108 in accordance with embodiments of the presentinvention.

The invention, however, is not limited to the description providedherein with respect to flowchart 600. Rather, it will be apparent topersons skilled in the relevant art(s) after reading the teachingsprovided herein that other functional flows are within the scope andspirit of the present invention. The flowchart 600 will be describedwith continued reference to the example cable modem system 100 of FIG.1.

At step 605, the cable modem 108 receives one or more data packets fromthe user device 116. The data packets include a payload comprisinganywhere from 1 to N bytes, depending on the type of data being sent. Inaccordance with the present invention, the data packets can be generatedby an application program running on the user device 116 described abovein reference to FIG. 1. For example, an application program running onthe user device 116 may generate voice or data information fortransmission over the HFC network 110. This voice or data informationcomprises the payload portion of the data packets.

At step 610, the cable modem 108 determines if the payload of the datapackets can be compressed in accordance with the present invention. Inmaking this determination, the cable modem 108 searches each payload toidentify any data strings contained within the payload that are listedin the data compression dictionary.

In step 615, if any data strings contained within the payload are foundlisted in the lookup table of the data compression dictionary, thencontrol is passed to step 625 so that the data strings can becompressed. In this way, the cable modem 108 will only compress apayload having data strings listed in the lookup table of the datacompression dictionary. If no data strings are listed, control passesimmediately to step 635 and the full payload (i.e. uncompressed datastrings) of the data packet is transmitted by the cable modem 108.

At step 625, the cable modem 108 will replace the data strings withineach payload with the binary tokens corresponding to the data stringslisted in the data compression dictionary.

At step 630, the cable modem 108 will append a compression indicator toeach token within the payload portion of the PDU data packet. Thisindicator serves as a signal to the CMTS that the payload portion of thePDU data packet has been compressed and that the data compressiondictionary will need to be referenced. The compression indicatorcontains a value indicating the length (number of bytes) of the token.By communicating the length of the token, the compression indicator alsosignals the CMTS where the compressed data string begins and ends.

At step 635, the cable modem 108 transmits those data packets having afull payload and those data packets having compressed payloads to theCMTS 104 over the HFC network 110.

In an embodiment, prior to step 605, the cable modem 108 would have beenturned on and a handshaking routine initiated with the CMTS 104 via theHFC network 110. During this initialization process, the cable modem 108would be provided with the data compression dictionary. In this way, thecable modem 108 is provided with the most current version of the datacompression dictionary prior to sending any packets.

3. Packet PDU Expansion

FIG. 7 is a flowchart of a method for expanding data packets using adata compression dictionary in accordance with embodiments of thepresent invention.

At step 705, the CMTS 104 receives a plurality of data packets.

At step 710, the CMTS examines the data packets to determine if any ofthe payloads have been compressed. If a compression indicator is found,then the CMTS 104 knows that the payload has been compressed. If nocompression indicator is found, then the payload is not suppressed andthe payload is processed according to standard protocols.

Once the CMTS 104 has identified the payloads that have been compressed,then at a step 715, the CMTS 104 searches the lookup table of its datacompression dictionary to identify the binary tokens matching the one ormore tokens contained in the payloads. The length of the compressed data(i.e., binary tokens) is determined by the value stored in thecompression indicators.

At step 720, the CMTS 104 expands each payload. To do so, the CMTS 104will overwrite the binary tokens within each payload with the expandeddata string corresponding to the binary token as listed in the lookuptable of the data compression dictionary. In expanding each payload,CMTS 104 produces a PDU data packet matching that previously presentedin step 605 of FIG. 6.

-   D. Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method for generating a data compression dictionary and utilizingit to enhance communication efficiency in a DOCSIS compliant network,comprising the steps of: i. identifying a plurality of frequentlyoccurring data strings transmitted by a plurality of cable modems in theDOCSIS network; ii. assigning a token to represent each one of theplurality of frequently occurring data strings; iii. entering each oneof the plurality of frequently occurring data strings and each tokenassigned to represent each one of the plurality of frequently occurringdata strings into a lookup table to produce a data compressiondictionary; and iv. transmitting the data compression dictionary to theplurality of cable modems in the DOCSIS network during initialization ofeach of the plurality of cable modems. 2-11. (canceled)